Opioid receptors in Hypoxia: –
Opioid receptors in Hypoxia are stimulated by endogenous endorphins, which usually cause analgesia and feelings of well-being. Opioids are used clinically, mainly as analgesics. Opioids differ in their receptor activity, and some (eg, buprenorphine) have combined agonist and antioxidant actions.
Histotoxic hypoxia: –
Histotoxic hypoxia (also referred to as histo-toxic hypoxia) is that the inability of cells to require or use oxygen from the bloodstream, despite physically normal delivery of oxygen to such cells and tissues. Histotoxic hypoxia results from tissue poisoning, like cyanide (which works by inhibiting cytochrome oxidase) and a few other toxins like sulfide (a by-product of sewage and tanning of leather).
In this form of hypoxia, the lungs are in perfect working condition, but the oxygen-carrying capacity of the blood is reduced. As the name itself suggests, anemia is a very effective way of causing anemic hypoxia. Carbon monoxide produces anemic hypoxia – as it binds Hb with such high affinity, preventing oxygen from binding, it reduces the oxygen-carrying capacity of the blood. Tissues do not get enough oxygen to maintain their metabolic needs because the blood is not carrying it. Arterial Po2 is normal but the amount of Hb available to carry O2 is small
Hypercapnia means excess carbon dioxide in the body fluids. Hypercapnia usually occurs in association with hypoxia only when the hypoxia is caused by hypoventilation or circulatory deficiency. The transport capacity of the blood for carbon dioxide is more than that for oxygen so that the resulting tissue Hypercapnia is much less than the tissue hypoxia. Serious Hypercapnia usually does not occur at the same time because carbon dioxide diffuses 20 times as rapidly as oxygen. If Hypercapnia does begin to occur, this immediately stimulates pulmonary ventilation, which corrects the Hypercapnia but not necessarily the hypoxia. When the alveolar Pco2 rises above 60 to 75 mm Hg – breathing becomes rapid and deep – “air hunger” – dyspnea becomes severe.
MECHANISMS OF HYPERCAPNIA -alveolar hypoventilation • -respiratory failure • -cerebral blood vessels are the most sensitive to CO2, PCO2 • -the adaptive value of increasing blood pressure brings more blood to the brain • -bring more CO2 to the lungs and attempt to excrete more • -CO2 narcosis – when CO2 is above 80-90 mmHg, decrease ventilation by ½
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Hypoxic brain injuries
Hypoxic brain injuries:- are brain injuries that form due to a restriction on the oxygen being supplied to the brain. The restricted flow of oxygen causes the gradual death and impairment of brain cells. This type of hypoxia is known as ischemic or stagnant hypoxia in which the blood flow to a tissue is so low that adequate O2 is not delivered to it despite a normal PO2 and hemoglobin concentration. Ischemic hypoxia ( or “stagnant hypoxia”) – Reduced brain oxygen is caused by inadequate blood flow to the brain. Stroke, shock, cardiac arrest, and heart attack may cause stagnant hypoxia. Ischemic hypoxia can also be created by pressure on the brain.
Tissue or Histotoxic Hypoxia
Tissue or Histotoxic Hypoxia: – O2 delivered to the tissues is normal but the tissues cannot utilize o2. hypoxia in tissues: –
ll cause a major drop in mitochondrial